Dalle parole del vicedirettore del Fermilab
Young-Kee Kim, in riferimento agli esperimenti previsti, sembra che tutto
proceda per il meglio:"We're in very good shape for the next 10 years, for
neutrino and muon programs."

Thursday, April 26, 2012

I am far to be an expert on the subject. I cannot really judge the scientific relevance of this talk. I would like to hear some opinions from people that work in the field or at least are closer than me on these topics.

Here we are. The launch of the NuSTAR satellite, initially scheduled for PI day this year (03/14), will happen around June 13th. The reason for this slip was an update of the software in the Pegasus rocket that will launch the satellite.
This "cheap" (a Small Explorer mission, that cost less than 200 million dollars) telescope will be launched in space inside a Pegasus rocket and extend its 10-meter long deployable mast to provide images of the sky in the so-called hard X-rays, meaning X-rays at higher energies than it was possible with the current X-ray imaging satellites.
Is it a sort of a worthless "My satellite is harder than yours" competition stealing money from taxpayers?
'Course not.

Wednesday, April 25, 2012

Tuesday, April 24, 2012

I am not sure that we all realized the sutble change that happened around the time we started using mathematics to describe reality. It is very "inter-esting" to suddenly realize that physics is mostly about "how". If the universe works as a clock, with a precise and never-failing rigorous mechanism behind, there is one unambiguous answer to the "how" question.The "why" is very intrincate to answer. Bodies fall, we know how, we can precisely determine the position at all times from initial conditions. To know why they fall...well, I think Feynman does it better than anyone could, watch him in action

...and yet, wouldn't we all agree that our insights all occur when trying to understand the "why" part of the question?

In modern science, real numbers play such a fundamental role that it is difficult to imagine a world without real numbers. Nevertheless, one may suspect that real numbers are nothing but a human invention. By chance, humanity discovered over 2000 years ago that our world can be understood very accurately if we phraze its laws and its symmetries by manipulating real numbers, not only using addition and multiplication, but also subtraction and division, and later of course also the extremely rich mathematical machinery beyond that, manipulations that do not work so well for integers alone, or even more limited quantities such as Boolean variables.

Now imagine that, in contrast to these appearances, the real world, at its most fundamental level, were not based on real numbers at all. We here consider systems where only the integers describe what happens at a deeper level. Can one understand why our world appears to be based on real numbers?

Monday, April 23, 2012

During the weekend I though it could have been a good experiment having a small "journal club" on papers submitted daily on the arXiv (i'll write something on arXiv one of these days). I cannot promise this blog-review will be very regular, but i'll do my best for the gr-qc and hep-th sections. Other contributors are in charge for other sections.

Our idea is to pick selected papers and describe them very briefly and informally. This brings me to the next problem: selecting the papers.

ArXivwise, Monday is usually quite a boring day. Papers appearing on Mondays are those submitted during the weekend and this explains why there are (on average) less papers. Well, not today!

Today the choice was quite hard (and not only because Frank Wilczek's "A Long View of Particle Physics"). Anyway my choice goes to Kent Yagi's paper above, which (or probably also because) is closely related to some projects I'm recently involved to.

Yagi is interested in constraining "alternative theories of gravity", i.e. theories that modify General Relativity (GR) in some regime. Typically, alternative theories differ from GR in the description of the dynamics of black holes, neutron stars and other compact objects, but they are conceived in such a way that they pass Solar System tests. I'll postpone the motivation to investigate these theories and my personal interest for them to a future post, for the time being let me just say that it is very hard to modify GR in a way that is compatible with current and past experiment.

In brief, the paper above discuss: (i) a way to put very stringent constraints (in fact, much more stringent than those coming from Solar System experiments) to a particular class of theories that modify GR in the strong-curvature regime and (ii) that, despite these strong constraints, these theories "could" explain an unexpected astrophysical result: apparently, the orbital separation of some binary system (i.e. the distance between two compact objects orbiting each other) decreases in time faster than what is predicted in GR. That the distance decreases is well-known: it is due to the emission of gravitational waves (GWs) from the system. The fact that the this decrease is faster than expected, points to some poor understanding of the astrophysical processes involved in the process or to a more copious emission of GWs than what expected in GR. A quite common feature of modified gravities is that they predict a more efficient GW emission but (iii) the results of this paper would be very difficult to obtain by considering a alternative theory other than what Yagi considers. This should come as a surprise, given the ridiculously large number of proposed alternatives but, on the other hand, it makes the results more interesting.

As the author stresses all over the paper, the cause of this discrepancy is most probably of astrophysical origin. However, it's intriguing to observe that current observations do not rule possible deviations from Einstein's theory at astrophysical level and, most importantly, that these corrections may eventually play a role in explaining the dynamics of compact stars and black holes [i'm sure the astro-contributors won't agree with me here :)]

"Physicists can point to technological spin-offs from high-energy physics, ranging from synchotron radiation to the World Wide Web. For promoting invention, big science in this sense is the technological equivalent of war, and it doesn’t kill anyone. But spin-offs can’t be promised in advance."